2004 trailblazer tach wire
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=101362
Printed Date: August 25, 2025 at 4:54 AM
Topic: 2004 trailblazer tach wire
Posted By: jslayton
Subject: 2004 trailblazer tach wire
Date Posted: January 19, 2008 at 12:02 PM
I am installing a remote start on a 2004 Trailblazer and it says that pin 49 on the blue plug on the PCM is for the Tach, but pin 49 doesn't have a wire coming out of it??? Is this normal??
Also, the remote start that I am using has three wires for unlock and three wires for lock. The three wires are labeled 87, 87a, and 30. The GMDL-BP module that I have says that it needs a ground pulse for the unlock input and ground pulse for the lock input. If I read the relay diagram correctly, I should be able to connect the 30 from the lock and 30 from the unlock to the corresponding wire on the GMDL-BP, then ground the 87 wire on both the unlock and lock set and it should pulse ground, correct?
Replies:
Posted By: sparkie
Date Posted: January 19, 2008 at 12:19 PM
You are correct for the door locks. There is only one white wire in the blue plug of the PCM. This is the tach wire. Do not use the WHITE/ black wire.
-------------
sparky
Posted By: StealthEs
Date Posted: January 19, 2008 at 12:20 PM
theres one of 2 tach wires for this car depending on the engine. 4.2L: The PCM is attached to the driver side of the engine. Tach is in the blue plug, pin 49. 5.3L: The PCM is near the lower front driver side of the engine. Tach is in the green plug, pin 10. ------------- Cris
Posted By: jslayton
Date Posted: January 19, 2008 at 12:27 PM
The pins are numbered on the back of the connector once and pin 49 has no wire. So I should just find the white wire?? Also, on this car, what can I use for the door trigger. The dome lights have a delay on them, so I don't think I can use that can I?
Posted By: jslayton
Date Posted: January 19, 2008 at 12:29 PM
Nevermind, I was looking at the wrong pin, I found the tach wire, but still need to know about the door trigger.
Posted By: KarTuneMan
Date Posted: January 19, 2008 at 12:58 PM
| DOORPIN | SEE NOTES | | | | | | You can use the GRAY/BLACK at the courtesy light under the dash or the light over the driver's side door to catch all doors and the rear hatch. The seperate doorpins are: GRAY/BLACK-driver's door (located in driver's door), BLACK/ WHITE-passenger door (located in passenger door), LT.BLUE/BLACK-left rear door, LT.GREEN/ BLACK-right rear door (both found at the fusebox under the rear seat on the driver's side. All wires are negative (-) polarity. |
|
-------------
Posted By: jslayton
Date Posted: January 19, 2008 at 1:08 PM
Thanks, two more questions. My alarm has two outputs for parking lights. Both output 12 volts. I was wondering if I could connect one of them to the hazard wire and then one to the headlight wire, or would I need to connect directly a parking light wire??
2nd question, do these cars come with a factory system? My mom said that she has opened the doors without unlocking them first and the horn started beeping, but she doesn't have a keychain module with it.
Posted By: KarTuneMan
Date Posted: January 19, 2008 at 1:18 PM
Parking lights are (POS)+ Brown under the steering column. Use just that one. Use the output thats stated for "parking light flash" How do you open a door with out unlocking it?  Your bypass should control the arming, and disarming of the factory security. -------------
Posted By: jslayton
Date Posted: January 19, 2008 at 2:04 PM
I don't see a courtesy light under the dash. Is it on the driver side or passenger??
Posted By: tedmond
Date Posted: January 19, 2008 at 6:02 PM
1)Thanks, two more questions. My alarm has two outputs for parking lights. Both output 12 volts. I was wondering if I could connect one of them to the hazard wire and then one to the headlight wire, or would I need to connect directly a parking light wire?? the reason there might be 2 parking light outputs is because some cars have 2 independant flashers eg one controls front and other for rear or left.right. 2) 2nd question, do these cars come with a factory system? My mom said that she has opened the doors without unlocking them first and the horn started beeping, but she doesn't have a keychain module with it. well gee, i wouldnt know how you open a door without unlocking...im just as confused kartuneman ! anyways, the only reason it would HONK is because the factory arm is still set and hasnt been disarmed. the car/factory alarm thinks some1 broke in and it will wail on you. as KTM mentioned, the GMDL-BP should be able to diarm/arm it for you.
|